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Thread: Hot Start Woes: Maybe NOT Fuel Pressure?

  1. #1
    Junior Member ASquared150's Avatar
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    Hot Start Woes: Maybe NOT Fuel Pressure?

    So Iíve completed the holy trinity of fuel pressure-related hot start issue fixes:

    New Fuel Accumulator ✓
    New Check Valve ✓
    New Primary Pressure Regulator O-Ring ✓

    ...all to no avail. Nothingís leaking, the car starts just fine cold and runs well too. But if it gets warmed up and turn it off it still refuses to start back up until itís completely cooled down again.

    So - if itís not a fuel pressure problem, what else could it be? OR is it still a fuel pressure problem and thereís something Iím missing?

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    You need to test how long you hold rest pressure. Just take the air cleaner off and lightly tap the air plate to know if there is still pressure. Then you time how long you hold pressure after engine shutdown.

    Of course using a pressure gauge is better but it sounds like you don't have one.

    How long you need to hold rest pressure depends on what the air temp is that day. I found in the summer above 90 deg. F I would get a hot start problem at 3 hours after shut down. Now if I could hold rest pressure for 3 hours or more I would not have that problem.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Junior Member ASquared150's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    You need to test how long you hold rest pressure. Just take the air cleaner off and lightly tap the air plate to know if there is still pressure. Then you time how long you hold pressure after engine shutdown.

    Of course using a pressure gauge is better but it sounds like you don't have one.

    How long you need to hold rest pressure depends on what the air temp is that day. I found in the summer above 90 deg. F I would get a hot start problem at 3 hours after shut down. Now if I could hold rest pressure for 3 hours or more I would not have that problem.
    Once I have that figured out though what do I do with the information? Do certain time ranges of holding rest pressure point to different problems/solutions?

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    Quote Originally Posted by ASquared150 View Post
    So Iíve completed the holy trinity of fuel pressure-related hot start issue fixes:

    New Fuel Accumulator ✓
    New Check Valve ✓
    New Primary Pressure Regulator O-Ring ✓

    ...all to no avail. Nothingís leaking, the car starts just fine cold and runs well too. But if it gets warmed up and turn it off it still refuses to start back up until itís completely cooled down again.

    So - if itís not a fuel pressure problem, what else could it be? OR is it still a fuel pressure problem and thereís something Iím missing?
    You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
    Rob

  5. #5
    Not really banned Michael's Avatar
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    Had the car been recently worked on before this hot start issue(for anything)? There is a reason I'm asking.

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by ASquared150 View Post
    Once I have that figured out though what do I do with the information? Do certain time ranges of holding rest pressure point to different problems/solutions?
    Your result will tell you if it is a rest pressure problem or to look elsewhere for the problem.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
    Junior Member ASquared150's Avatar
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    Quote Originally Posted by PJ Grady Inc. View Post
    You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
    Rob
    Yup that’s the one I changed the other larger one was fine. Honestly the one on the plunger cup looked like it was in good shape too but I had the replacement so I made the switch.

    Maybe I should also mention that I did all three separately. I did the fuel accumulator last week. When that didn’t work I made the trip out to DMC Midwest and picked up the check valve and o-ring. Did the check valve this morning and still had the hot start problem so did the o-ring this afternoon.

    The car has a new (old-style) fuel pump as of last October and a fresh fuel filter. Seriously grasping at straws for what the issue is. Maybe something weird with the cold-start injector?
    Last edited by ASquared150; 03-10-2018 at 10:26 PM.

  8. #8
    One of those purists you keep hearing about. sdg3205's Avatar
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    Quote Originally Posted by PJ Grady Inc. View Post
    You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
    Rob
    I've had an issue with the 3rd o-ring. on the base of the needle, which you can only find after complete disassembly! Check your CSV and injectors for leaking out your rest pressure too.
    Dave

    Here, somewhere.


  9. #9
    Senior Member DMC5180's Avatar
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    Quote Originally Posted by ASquared150 View Post
    Maybe something weird with the cold-start injector?
    The next time you go to do a Hot start and it doesnít, unplug the blue CSV connector and try again. IF it starts, this is an indicator that the TTS has been bypassed to ground and the engine is getting too much fuel when hot.



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    DENNIS

    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  10. #10
    Senior Member Rich's Avatar
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    Quote Originally Posted by ASquared150 View Post
    Maybe something weird with the cold-start injector?
    About initial diagnosis question: If you or DMCMW can verify that the system holds at least 25psi for 10 minutes after engine shutoff then you'll know if you need to keep troubleshooting for fuel leakage or work on non-pressure causes. The air meter plate test is a good starting point but you can't get a number from that.

    About your CSV question: Agreeing with Dennis on the TTS check and adding this. Among the potential leak points, most of which are mentioned in the thread already, is the CSV. If it leaks enough - or if any of the injectors leak - then the system won't hold rest pressure. So, is it possibly a leaky CSV? Yes, but not likely. You could pull it and look for fuel leaking with ignition ON, engine off, TTS & CSV plugged in as usual.

    Be safe around pressurized fuel components.
    Last edited by Rich; 03-11-2018 at 12:06 PM.
    March '81, 5-speed, black interior

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